The present invention is related to a method and apparatus for plating semiconductor chip headers in general and, in particular, to a method and apparatus for plating header posts.
A typical semiconductor chip header includes a body member. The body member comprises an insulating material encased in a metallic envelope for forming a chip receiving surface on the top thereof. Extending from the bottom of the body member is a plurality of leads. Normally one of the leads, called for convenience an envelope lead, is electrically connected to the envelope for providing an electrical connection to a chip bonded to the top of the envelope. The others of said plurality of leads are disposed to pass through said header body and are electrically insulated from said envelope for forming posts on the top thereof. The posts are typically located outwardly of the chip receiving area and are provided to be connected, in the course of fabricating a solid state device, to selected parts of the chip as by thin wires or the like.
In the process of fabricating semiconductor devices, it is frequently necessary to plate the posts. Heretofore, this has been done by inserting the headers in an inverted position in individual holes in the bottom of a supporting container or belt such that the posts of the headers and a portion of the body project downwardly therethrough. The posts and the portion of the header body projecting through the holes are then immersed in a plating solution.
For the plating process to occur, it is necessary to provide an electrical potential between the posts and the plating solution such that a current will flow therebetween. For convenience and because there has been no prior known way to simply and economically make an electrical contact between the posts alone and the bath, it has been the practice to place one electrode in the bath and another in electrical contact with the header leads. Because of the number of leads and the lack of any prior known practical way to separate them economically, it has been the practice to make the electrical contact with the leads using a fluid or powdered electrolyte. When doing this, however, both the thru-leads and the envelope lead are electrically connected. This results in plating not only the posts but also that portion of the header extending with the posts through the supporting belt or container.
Frequently, for some applications, only the posts require plating with a precious metal. In other applications, the header chip receiving area may be plated with one type of precious metal and the posts with another type of precious metal. In either case, if the precious metal required for the posts can be restricted to the posts in the plating process, it is obvious that a considerable savings in the cost and use of precious metals is possible.